Method of making mercury switches



y 1934! c. H. LARSON 1,967,949

' METHOD OF MAKING MERCURY SWITCHES Filed Jan. 5, 1953 6A5 FILL PatentedJuly 24, 1934' UN TED STATES lVIETHOD OF MAKING MERCURY SWITCHES Carl H.Larson, Elkhart, Ind., assignor to The Adlake Company, a corporation ofIllinois Application January 3, 1933, Serial No. 649,819

6 Claims.

The usual method of making mercury switches is to take an open switchenvelope into which electrodes have been sealed, place a quantity ofmercury in the envelope along with any other a parts which are to gointo the switch, evacuate the envelope, introduce a suitable gas fill,and then seal-oif the open end of the envelope. The switch is thentested, and if it fails to perform satisfactorily, the seal is brokenand the necessary adjustments are made, suchas' varying the amount ofmercury, repositioning the electrodes, etc. The envelope is againevacuated, filled with an inert gas and then sealed off and another testis made. This process of opening and closing the switch envelope isrepeated as often as necessary to obtain the desired characteristics ofthe switch.

Certain kinds of mercury switches require greater accuracy in theirmanufacture than others, because of more stringent service requirements..For example, switches which are used in relays'must be highly sensitiveso that the pickup-and drop away values of the relay will not vary. Timedelay switches also require great accuracy in their manufacture becauseof the fine adjustments which must be made to obtain given time delays.

In the switch which has been chosen to illustrate the method of thisinvention, a hollow plunger is placed within a vertical switch envelopeinto which suitable electrodes have been sealed, and by magneticallymanipulating the position of the plunger in the envelope, the mercurylevel may be controlled to open or close a circuit through theelectrodes. The top of the plunger is closed except for a smallrestricted opening into which'a. tapered plug is fitted. When theplunger is lifted by energizing the associated coil, mercury is carriedup in the plunger and slowly recedes as the gas pressure within theplunger is equalized with the outside pressure by gas entering theplunger'through,

the time delay in such a switch will be by testing the switch in openair, prior to inserting the gas fill and sealing. This is due to thefact thatgases commonly used for fills pass through re-- strictedorifices much faster than air. Other variables, such as humidity,viscosity of the mercury, and mercury friction also prevent accuratedeterminations of time delay prior to sealiig.

Even if it were possible to control conditions of humidity, rates of gasleakage, viscosity, etc. it would still be undesirable to test theswitch in the open atmosphere.- A single operation of the circuitbreaker in the open air, would so contaminate the mercury that it wouldcause the switch to be erratic in later operation.

The principal object of the present invention, therefore, is to providea method and apparatus for making mercury switches that avoids thenecessity of breaking open the switch seals in order to makeadjustments; that enables greater accuracy to be obtained in securinggiven time delays; that saves material, reduces the cost of manufacture,and enables switches to be made in less time than heretofore possible;and that effects these desirable results by the use of simple apparatus.

-Further and other objects and advantages will become apparent as thedisclosure proceeds and the description is read in conjunction with theaccompanying drawing, in which Fig. 1 is a semi-diagrammatic viewshowing a switch in the process of manufacture according to theteachings of this invention;

Fig. 2 is a sectional view showing a completed switch in operativeposition within a relay coil; and

Fig. 3 is a perspective view of the adjustable plug in the top of theswitchplunger.

The description of a specific switch structure and a preferred methodare for the purpose of disclosure only and should not be construed asimposing limitations upon the appended claims except as may be requiredby the prior art.

An understanding of the method of manufacturing mercury switchesaccording to this invention will be facilitated by first describing thecompleted switch and the manner in which it is used. Referring,therefore, to Fig. 2, it will be, seen that the switch comprises avertical glass envelope 10 into the bottom of which electrodes 11 and 12are suitably sealed. A glass sleeve 13 insulates the electrode 11 fromthe mercury fill 14 up to a point just below the top of the electrode.The electrode 12 is uninsulated and is constantly immersed in themercury.

A plunger, or displacer 15, which may be made of iron or iron and someother material, displaces suflicient mercury when in the position shownin Fig. 2 to cover the top of the electrode 11 and thus establish aconnection between the electrodes 11 and 12. When the plunger-is liftedby energizing the coil 16 which is telescoped over the switch, themercury recedes a sufficient amount to uncover the electrode. 11 andbreak the circuit through the electrodes 11 and 12.

The coil 16 is wound on a spool 17 having a central opening 18 ofsuificient diameter to receive pole sleeves 19 and 20. The pole sleevesmay be adjusted vertically within the spool and are clamped in place byclips 21 which are secured to the ends of an iron yoke 22. The yokeincreases the operating efiiciency of the coil by furnishing an exterioriron circuit and preferably is laminated for use with alternatingcurrent. The position of the sleeves 19 and 20 within the spool 18determines the position of the air gap in the magnetic circuit. When thecoil is energized, the plunger 15 rises in its eiTort to close the airgap and the mercury level drops in the envelope, thereby uncovering theelectrode 11.

The top of the plunger 15 is closed except for a small opening 23 intowhich a tapered plug 24 is tightly fitted. The plug is shown moreclearly in Fig. 3. Instead of a single restricted opening in the top ofthe plunger, a porous material, such as a ceramic, might be substitutedfor the plunger head.

Springs 25 and 26 cushion the plunger against hard impacts with the topand bottom of the switch envelope. Preferably the switch plunger has thebulk of its mass above the mercury level in order to make the potenialenergy of the plunger when in its raised position substantially equal tothe magnetic energy necessary to raise the plunger from its depressedposition.

Obviously the tighter the fit between the plunger 15 and the plug 24,the less will be the gas leakage between the interior and exterior ofthe plunger. It is this adjustment which must be made with greataccuracy in order to obtain given time delays.

Referring now to: Fig. 1, which illustrates preferred apparatus for useof the method, the switch envelope 10 with electrodes Hand 12 sealedinto the bottom, is first filled to a level 27 with mercury. The plunger15 is then placed in the envelope with the plug 24 approximatelypositioned in the opening 23 according to the time delay that isrequired. The envelope is then ready for evacuation.

A vacuum pump diagrammatically shown at 28 is joined by a suitableconnection 29 to a.

three-way glass stop cook 30, which in turn is connected to a highfrequency discharge device 31 and a piece of glass tubing 32 having arestricted portion 33. The connection between the envelope and glasstubing 32 is made by a heavy piece of rubber tubing 34, and a similarpiece of rubber tubing 35 connects the discharge device 31 with theupper end of the tubing 32. Suitable connections 9 and 36 join thedischarge device 31 with the stop cook 30 and the stop cock with theconnection 29, respectively. I

The stop cock is providedwith a plug 37 with two holes 38 and 39 boredat an angle adapted to connect the nipple 40 with the nipple 41, or thenipple 42 with the nipple 41, according to the position of the plug. Inthe position shown in Fig. 1, the nipple 41 is connected to the nipple42.

The high frequency discharge device 31 includes a spark coil 43connected to a suitable source of current and having one lead 44grounded and the other lead 45 connected to an electrode 46. When thecoil 43 is in operation, the degree of vacuum in the system can bedetermined by the color of the discharge. The color ranges from a deeppurple when the system is partially evacuated to a light blue when ahigh vacuum has been obtained.

After the vacuum pump 28 has reduced the pressure amount, the stop cook30 is rotated through 180 to the position shown in Fig. 1. In thisposition, a suitable gas fill is introduced into the envelope from thecontainer 47. The gas may be helium, hydrogen, nitrogen, or any othersuitable gas.

The top of the container 47 is fitted with a valve 48, and gauge 49, theformer for regulating the pressure of the gas being emitted from thecontainer, and the latter for registering that pressure. The nipple 40of the stop cook 30 is joined by a connection 50 with the container 4'7and a valve 51 is provided in the connection for regulating the flow ofgas therethrough' A gauge 52 interposed between the valve 51 and thestop cock registers the pressure in the envelope 10.

In practice, the envelope is evacuated and filled with gas from thecontainer several times in order to make sure that all air has beenremoved from the envelope. The envelope is finally filled with gas at apressure of about five pounds less than atmospheric pressure, and thenthe envelope is sealed oiT at 33. This forms a temporary switchstructure in which the actual conditions of use are exactly'duplicated,and the switch may then be inserted in a suitable coil for testing. Ifit is found that the mercury level is too high or too low, or the plug24 does not provide the required time delay, the connection at 34 may bein the switch envelope a sufficient broken, the plunger removed and thenecessary I adjustments made. Thereafter the process is repeated untilthe switchiunctions according to specification. The switch envelope 10is then sealed off in the usual manner below the connection 34.

Although it is usually desirable to seal ofi the temporary switchstructure at 33 so as to conduct the tests in a more convenient place,it is not at all necessary that it be done. It is obvious that by merelyclosing the stop cook 30, it is possible to test the switch by placing asolenoid in appropriate position over the envelope. In such case thetubing 32 is unnecessary.

The process is readily adaptable to mass production methods. Forexample, a number of switch blanks may be placed on a rotary table forautomatic evacuation and filling, after which tests may be made on theindividual switches without removing them from the table. Whenever aswitch is found to have the proper operating characteristics, it maythen be sealed off and removed from the table.

Various modifications of the process will be apparent to those skilledin the art. For example, it is not essential, in every instance, thatthe envelope be separated from the associated apparatus to makeadjustments in the switch when tests have found them necessary, it beingpossible to provide suitable means within the envelope for subject of acopending application filed July 6, 1932 and bearing Serial Number621,088.

What I claim is:

1. A method of making mercury switches which includes taking an openswitch envelope into which electrodes have been scaled, placing aquantity of mercury and a displacer in the envelope, temporarilyconnecting the open end of the envelope through a piece of glass tubingwith apparatus for evacuating the envelope and for thereafter filling itwith an inert gas and then sealing off the tubing to produce a temporaryswitch structure which duplicates the characteristics of a finishedswitch, testing the temporary switch and adjusting it to specification,and finally sealing off the open end of the envelope to form a completedswitch.

2. The method of making a time delay mercury switch of the type in whichthe escapement of gas through one or more restricted passagesconstitutes the timing element, said method including taking an openswitch envelope into which electrodes have been sealed, placing aquantity of mercury and a mercury displacer in the envelope, connectingthe open end of the envelope with apparatus adapted to produce in theenvelope the gaseous conditions which exist in a finished switch,producing such conditions, and then testing the switch and adjusting thesize and/or number of passages through which the gas escapes to obtainpredetermined switch characteristics, and then sealing of! the open endof the switch.

3. The method of making a mercury switch which includes taking an openswitch envelopeinto which electrodes have been sealed, placing aquantity of mercury and a mercury displacer in the envelope, connectingthe open end of the envelope, through a piece of glass tubing, withapparatus adapted to produce in the envelope the gaseous conditionswhich exist in the finished switch, and then sealing off the glasstubing to produce a temporary switch structure which duplicates thecharacteristics of the finished switch, testing the temporary switch andadjusting it to specification, and finally sealing off the open end ofthe envelope to form a completed switch.

4. The method of making a mercury switch which includes taking an openswitch envelope into which electrodes have been scaled, placing aquantity of mercury and a mercury displacer in the envelope, connectingthe open end of the envelope, through a piece of glass tubing having arestricted passage, with apparatus adapted to produce in the envelopethe gaseous conditions which exist in the finished switch, and thensealing off the restricted portion of the glass tubing to produce atemporary switch structure which duplicates the characteristics of thefinished switch, testing the temporary switch and adjusting it tospecification, and finally sealing off the open end of the envelope toform a completed switch.

5. The method. of making mercury switches which includes taking an openswitch envelope into which electrodes have been scaled, placing aquantity of mercury in the envelope, connecting the open end of theenvelope with apparatus adapted to produce in the envelope the gaseousconditions which exist in the finished switch, producing suchconditions, and then testing the switch, adjusting themercury level andother parts until proper switch characteristics are obtained, and thensealing oil the open end of the envelope.

6. The method of making mercury switches which includes taking an openswitch envelope into which electrodes have been scaled, placing aquantity of mercury in the envelope, connecting the open end of theenvelope with apparatus adapted to produce in the envelope the gaseousconditions which exist in a finished switch, producing such conditionsand then testing the switch while the envelope is still connected to theapparatus, removing the connection and adjusting the mercury level andother parts, connecting the envelope to the apparatus again andrepeating the subsequent steps until proper switch characteristics areobtained, and then sealing off the open end of the envelope.

' I v CARL H. LARSON.

